The polyamides industry uses a whole range of monomers consisting of long-chain ω-amino acids, normally known as Nylon, characterized by the length of methylene chain (—CH2—)n separating two amide functional groups —CO—NH—. Thus it is that Nylon 6, Nylon 6,6, Nylon 6,10, Nylon 7, Nylon 8, Nylon 9, Nylon 11, Nylon 13, and the like, are known.
These monomers are, for example, manufactured by a chemical synthesis route using in particular, as starting material, C2 to C4 olefins, cycloalkanes or benzene but also castor oil (Nylon 11), erucic or lesquerolic oil (Nylon 13), and the like.
Current developments with regard to the environment are resulting in the use of natural starting materials originating from a renewal source being favored in the fields of energy and chemistry. This is the reason why some studies have been taken up to develop, industrially, processes using fatty acids/esters as starting material in the manufacture of these monomers.
This type of approach has only a few industrial examples. One of the rare examples of an industrial process using a fatty acid as starting material is that of the manufacture, from the ricinoleic acid extracted from castor oil, of 11-aminoundecanoic acid, which forms the basis of the synthesis of Rilsan 11®. This process is described in the work “Les Procédés de Pétrochimie” [Petrochemical Processes] by A. Chauvel et al., which appeared in Editions Technip (1986). 11-Aminoundecanoic acid is obtained in several stages. The first consists of a methanolysis of castor oil in a basic medium, producing methyl ricinoleate, which is subsequently subjected to a pyrolysis in order to obtain, on the one hand, heptanaldehyde and, on the other hand, methyl undecylenate. The latter is converted to the acid form by hydrolysis. Subsequently, the acid formed is subjected to a hydrobromination to give the ω-brominated acid, which is converted by amination to 11-aminoundecanoic acid.
The main studies have related to the synthesis of 9-aminononanoic acid, which is the precursor of Nylon 9, from oleic acid of natural origin.
As regards this specific monomer, mention may be made of the work “n-Nylons, Their Synthesis, Structure and Properties”, 1997, published by J. Wiley and Sons, chapter 2.9 (pages 381 to 389) of which is devoted to Nylon 9. This article summarizes the preparations and studies carried out with regard to the subject. Mention is made therein, on page 381, of the process developed by the former Soviet Union which has resulted in the commercialization of Pelargon®. Mention is also made therein, on page 384, of a process developed in Japan which uses oleic acid originating from soybean oil as starting material. The corresponding description makes reference to the work by A. Ravve “Organic Chemistry of Macromolecules” (1967) Marcel Dekker, Inc., part 15 of which is devoted to polyamides and which mentions, on page 279, the existence of such a process.
In order to be fully informed with regard to the state of the art on this subject, mention should be made of the numerous papers published by E. H. Pryde et al. between 1962 and 1975 in the Journal of the American Oil Chemists' Society—“Aldehydic Materials by the Ozonization of Vegetable Oils”, Vol. 39, pages 496-500; “Pilot Run, Plant Design and Cost Analysis for Reductive Ozonolysis of Methyl Soyate”, Vol. 49, pages 643-648, and R. B. Perkins et al., “Nylon-9 from Unsaturated Fatty Derivatives: Preparation and Characterization”, JAOCS, Vol. 52, pages 473-477. It should be noted that the first of these papers also makes reference, on page 498, to previous studies carried out by the Japanese authors H. Otsuki and H. Funahashi.
To summarize this part of the state of the art targeted at this type of synthesis of “Nylon 9” from vegetable oils, a description may be given of the following simplified reaction mechanism applied to the oleic ester extracted from the oils by methanolysis:
Reductive OzonolysisH3C—(CH2)7—CH═CH—(CH2)7—COOCH3+(O3,H2)→HOC—(CH2)7—COOCH3+H3C—(CH2)7—COHReductive AminationHOC—(CH2)7—COOCH3+(NH3,H2)→H2N—(CH2)8—COOCH3+H2OHydrolysisH2N—(CH2)8—COOCH3+H2O→H2N—(CH2)8—COOH+CH3OH
However, this route, which is very attractive from the reaction viewpoint, exhibits a significant economic drawback consisting of the production, during the first stage, of a long-chain aldehyde (9 carbon atoms in total) which is virtually nonrecoverable in value, in particular in the polymer industry relating to polyamides.
The UK patent No. 741 739 describes, for its part, the synthesis of this same acid from oleic acid but using the oleonitrile route. The simplified reaction scheme for this process is as follows. An analogous route is mentioned in the abovementioned paper by R. B. Perkins et al., p. 475.H3C—(CH2)7—CH═CH—(CH2)7—COOH+NH3→H3C—(CH2)7—CH═CH—(CH2)7—CN+2H2OH3C—(CH2)7—CH═CH—(CH2)7—CN+(O3+H2O)→H3C—(CH2)7—COOH+CN—(CH2)7—COOHCN—(CH2)7—COOH+2H2→H2N—(CH2)8—COOH
This synthesis results in pelargonic acid H3C—(CH2)7—COOH as byproduct.
The present invention is targeted at providing a novel process for synthesizing a whole range of ω-amino-alkanoic acids or their esters from natural unsaturated fatty acids.
The problem is thus that of finding a process for the synthesis of various ω-amino acids of formula H2N—(CH2)n—COOH (and of their polymers) in which n is between 3 and 14, starting from renewable starting materials (very widely accessible and therefore inexpensive), which is simple to carry out while avoiding, on the one hand, the environmental constraints mentioned above and, on the other hand, the economic handicaps due to the byproducts from the reactions.
The solution provided consists in working from starting materials consisting of natural long-chain unsaturated fatty acids, in converting them, in a first stage, into ω-unsaturated nitriles and in then subsequently, in a second stage, “reinserting” a carboxylic acid functional group into the compound by an action on the end double bond of the ω-unsaturated nitrile, either by means of oxidative cleavage or by a cross metathesis reaction with a compound of acrylate type.